Memory device having high speed sense amplifier comprising pull-up circuit and pull-down circuits with drivability for each

ABSTRACT

A sense amplifier is constructed to reduce the occurrence of malfunctions in a memory read operation, and thus degraded chip yield, due to increased offset of the sense amplifier with further sealing down. The sense amplifier circuit is constructed with a plurality of pull-down circuits and a pull-up circuit, and a transistor in one of the plurality of pull-down circuits has a constant such as a channel length or a channel width larger than that of a transistor in another pull-down circuit. The pull-down circuit with a larger constant of a transistor is first activated, and then, the other pull-down circuit and the pull-up circuit are activated to perform the read operation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 11/071,351filed Mar. 4, 2005 now U.S. Pat. No. 7,224,629.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese Patent ApplicationJP 2004-109598 filed on Apr. 2, 2004, the content of which is herebyincorporated by reference into this application.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a semiconductor memory device. Moreparticularly, the present invention relates to a low power consumption,high-speed, and highly integrated semiconductor memory device and to adifferential amplification operation of a semiconductor device in whicha logic circuit and a semiconductor memory device are integrated.

BACKGROUND OF THE INVENTION

The dynamic random access memory (hereinafter, referred to as DRAM)which is one example of the semiconductor memory device is mounted invarious types of electronic equipment used in our daily life, forexample, in a main memory of a large-scale computer and a personalcomputer and a work memory of digital electronics such as a cellularphone and a digital camera. In addition, with the increasing needs forthe lower power consumption and higher performance in the equipment inrecent years, the high-performance DRAM capable of achieving the lowpower consumption, the high-speed operation, and the large capacity hasbeen strongly demanded.

The most effective method to realize the high-performance DRAM is toscale down the cell transistors and the cell capacitors used in a memorycell of the DRAM. The scaling down of the cell transistors and the cellcapacitors makes it possible to reduce the size of the memory cell. As aresult, the length of the gate line is reduced and the parasiticcapacitance of the data line can be reduced. Consequently, the lowvoltage operation is enabled and the low power consumption can beachieved. Also, since the parasitic capacitance of the data line can bereduced, the sense amplifier can be operated at high speed. Furthermore,the merit obtained from the scaling down is significant, for example,the improvement of the performance of the equipment resulting from theincrease of the capacity of the memory. Therefore, the performance ofnot only the existing products but also the products under developmentcan be improved by the scaling down.

However, due to the further scaling down in the 0.1 um node or the 0.065um node and 0.045 um node like in the existing product, various sideeffects occur in addition to the above-described effects of theperformance improvement. The side effect includes the malfunction causedwhen reading a signal of the memory cell due to the variation in devicecharacteristics which is increased by the scaling down. In this case,the variation in device characteristics means, for example, thedifference in intensity of the threshold voltage of the cell transistorand the leakage current from the cell transistor (deviation from theaverage value). As described above, if the variation in devicecharacteristics is large, various problems occur. For example, the dataretention characteristics of the DRAM are degraded, and the yield of thechip is reduced. In particular, it is concerned that the variation inthreshold voltage of the sense amplifier circuit increases in thefuture. This is because the data line pitch of the memory cell is verynarrow in the recent DRAM and thus the size of the sense amplifiercircuit connected to the data line must be reduced in the layout.Therefore, the processing error of the transistors constituting thesense amplifier becomes large, and as a result, the variation inthreshold voltage of the pair transistor is increased. Usually, thisproblem is called the offset of the sense amplifier, and causes a largeinfluence on the performance of the DRAM. In addition, the problem ofthe offset of the sense amplifier is described in detail in “VLSI MemoryChip Design”, pp. 195 to 247, Springer, 2001 by Kiyoo Itoh, and it iswell known that the reduction of the offset greatly contributes to theimprovement of the yield of the DRAM. Therefore, for the achievement ofthe performance improvement by the scaling down, the circuit designwhich can achieve not only the reduction of the processing error butalso the reduction of the sense amplifier offset is required as animportant technology in the future.

As an example for the solution of the above-described problems,ISSCC2002 Dig. Tech. Papers, pp. 154 to 155 by Sang Hoon Hong et al.discloses the technology for canceling the sense amplifier offset. Inthis method, the precharge voltage of the data line is corrected byusing a current mirror operational amplifier. By doing so, the offset ofthe sense amplifier can be substantially reduced. However, since thenumber of devices added to the sense amplifier is vary large and thearea of the sense amplifier is increased in this method, the chip sizeis increased. In addition, since the control signals to be driven arealso increased, the timing margin is increased, and thus, the reductionof the operation speed is concerned. Also, “2003 symposium on VLSICircuits Dig. Tech. Papers, pp. 289 to 292” by Jae-Yoon Simm et al.discloses a charge-transfer type sense amplifier. In this method, thecharge accumulated in a peripheral circuit such as a sense amplifier istransferred to a data line on the memory cell side via a switchtransistor connected to the data line so as to generate large potentialdifference in the sense amplifier. Therefore, even when the offset ofthe sense amplifier is increased, since the potential difference largerthan the offset can be applied to the sense amplifier, it stands up wellto the variation and is superior in the low-voltage operation. However,also in this method, since a number of additional devices, for example,a precharge circuit and a switch transistor for rewriting are required,the chip size is increased.

SUMMERY OF THE INVENTION

Under the circumstance as described above, an object of the presentinvention is to provide a sense amplifier circuit which can be realizedwith a small number of additional devices, can be operated at highspeed, and can reduce the offset of the sense amplifier.

For the achievement of the above-described object, prior to the presentinvention, the inventors of the present invention have studied theinfluence caused by the offset of the sense amplifier on the readoperation and the configuration of the sense amplifier capable ofreducing the offset and realized with a minimum number of additionaldevices.

FIG. 18 is a diagram showing the circuit configuration of arepresentative DRAM. In FIG. 18, the memory cell MC is comprised of anaccess transistor TN0 whose drain is connected to a data line DLB and acell capacitor CS0 one electrode of which is connected to a source ofthe access transistor TN0. Note that the potential of L is retained inthe memory cell MC. A data line pair DLT and DLB connected to aplurality of memory cells is connected to a sense amplifier circuit SA0via a switch transistor SHR. The sense amplifier circuit SA0 iscomprised of a column switch YSW, a precharge circuit PCH, a pull-downcircuit NDRV, and a pull-up circuit PDRV. FIG. 19 shows a timingwaveform when reading the signal of the memory cell MC by using theconventional sense amplifier circuit SA0 of FIG. 18, which shows theoccurrence of the malfunction. First, the data line is precharged bydriving the precharge circuit PCH, and the precharge circuit PCH isnegated. Then, the switch transistor SHRL on the selection sub-arraySARY side is driven high and kept in this state, and the other switchtransistor SHRR is negated low. When the sub-word line WLO is asserted,the minute signal corresponding to L is outputted form the memory cellMC to the data line DLB, and the signal difference dvsig occurs in thedata line pair.

Thereafter, when a common source line CSN of the pull-down circuit NDRVand a common source line CSP of the pull-up circuit PDRV are driven to aground voltage VSS and a data line voltage BDL, respectively, the minutepotential difference dvsig represented by a broken line is amplified toa high level VDL and a low level VSS and is transferred to the circuitsof latter stages through the column switch YSW and the local data linesLIOT and LIOB. However, as described above, the further scaling downincreases the offset of the sense amplifier. For example, in FIG. 18,the difference VTN1-VTN2 between the threshold voltage VTN1 of the NMOStransistor TN1 and the threshold voltage VTN2 of the NMOS transistor TN2in the pull-down circuit NDRV becomes larger than the minute signaldifference dvsig, and at the same time, the difference VTP1-VTP2 betweenthe threshold voltage VTP1 of the PMOS transistor TP1 and the thresholdvoltage VTP2 of the PMOS transistor TP2 in the pull-up circuit PDRVbecomes larger than the minute signal difference dvsig in some cases. Insuch a case, since the data line DLT is driven to the L side morestrongly than the data line DLB, the reading malfunction occurs asrepresented by the solid line in FIG. 19.

For the prevention of the malfunction as described above, the method inwhich the constant of transistors constituting the pull-down circuitNDRV and the pull-up circuit PDRV is increased to reduce the offset andthe method in which a preamplifier function for amplifying the minutesignal difference dvsig to the voltage difference at least larger thanthe offset is added are available. More concretely, in the formermethod, the channel length and the channel width of the transistors TN1,TN2, TP1, and TP2 constituting the pull-down circuit NDRV and thepull-up circuit PDRV are simply increased to reduce the offset. In thismethod, however, the driving current of the sense amplifier circuit SA0is reduced due to the increase of the channel length and the accessspeed of the memory is reduced. On the other hand, as the latter methodof adding a preamplifier function, one more pull-down circuit NDRV isadditionally provided. If the added pull-down circuit is first driven topreamplify the data line to the voltage difference larger than theoffset of the original pull-down circuit and the pull-up circuit, thereading malfunction may be prevented.

In addition, the number of added transistors is small, that is, only twotransistors are added, and the increase of the area is reduced to theminimum. As a known example of this circuit configuration, JapanesePatent Application Laid-Open No. 7-226081 and Japanese PatentApplication Laid-Open No. 2-146177 disclose the sense amplifier circuitusing a plurality of pull-down circuits. In the method of thisdisclosure, the number of added circuits is small and the area overheadis also small. In these methods, however, although the high-speedoperation of the sense amplifier is considered, the reduction of theoffset to prevent the reading malfunction is not considered at all. Morespecifically, since the disclosed methods do not have the preamplifierfunction, the problem of the offset cannot be solved in principle.

Under the circumstance as described above, an object of the presentinvention is to reduce the sense amplifier offset which will beremarkable in the future and to prevent the reading malfunction. Also,another object of the present invention is to reduce both the offset andthe layout area of the sense amplifier circuit SA0.

The typical ones of the inventions disclosed in this application will bebriefly described as follows.

In a semiconductor memory device comprised of a plurality of memorycells and a plurality of sense amplifier circuits, the sense amplifiercircuit has at least two pull-down circuits. Also, one of the pull-downcircuits is first driven to amplify the data line to be larger than theoffset of the pull-down circuit and the pull-up circuit in the latterstage, and then, the pull-down circuit and the pull-up circuit in thelatter stage are driven. In this case, it is preferable that the channellength and the channel width of the transistors in the pull-down circuitdriven first are increased so as to reduce the offset of thetransistors. Furthermore, it is also preferable to form the senseamplifier from a plurality of pull-up circuits.

According to the present invention, in the semiconductor integratedcircuit including a plurality of memory cells and a plurality of senseamplifier circuits, the offset of the sense amplifier can be reduced. Asa result, the low-voltage operation and the high-speed reading operationcan be realized. Also, since the offset can be reduced, the length ofthe data line can be increased and the occupancy of the memory cell canbe increased. That is, it is possible to realize the highly integratedsemiconductor memory device.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 is a diagram showing the basic configuration of the senseamplifier circuit part of the semiconductor memory device according tothe first embodiment of the present invention;

FIG. 2 is a diagram showing an example of the bank comprised of senseamplifier circuits according to the first embodiment shown in FIG. 1;

FIG. 3 is a diagram showing an example of the operation waveform of thesense amplifier shown in FIG. 1;

FIG. 4 is a plan view showing an example of the layout of the senseamplifier array shown in FIG. 2;

FIG. 5 is a plan view showing an example of the layout of the senseamplifier array shown in FIG. 2;

FIG. 6 is a plan view showing an example of the layout of the memorycells shown in FIG. 1;

FIG. 7 is a cross-sectional view showing a part of the configuration ofthe bank shown in FIG. 2;

FIG. 8 is a block diagram of a semiconductor memory device comprised ofa plurality of sense amplifiers shown in FIG. 1;

FIG. 9 is a plan view showing a modified example of the layout of thesense amplifier array shown in FIG. 2;

FIG. 10 is a diagram showing an example of the operation waveform of thesense amplifier when the layout of the sense amplifier in FIG. 9 isused;

FIG. 11 is a diagram showing the circuit configuration of a negativesub-word driver;

FIG. 12 is a diagram showing an example of the operation waveform in thesecond embodiment in which the negative sub-word driver in FIG. 11 isapplied to the sense amplifier of the present invention;

FIG. 13 is a diagram showing the basic configuration of the senseamplifier circuit part of the semiconductor memory device according tothe third embodiment of the preset invention;

FIG. 14 is a diagram showing an example of the operation waveform of thesense amplifier shown in FIG. 13;

FIG. 15 is a plan view showing an example of the layout of the senseamplifier array comprised of a plurality of sense amplifiers shown inFIG. 13;

FIG. 16 is a diagram showing the basic configuration of the senseamplifier circuit part of the semiconductor memory device according tothe fourth embodiment of the preset invention;

FIG. 17 is a diagram showing an example of the operation waveform of thesense amplifier shown in FIG. 16;

FIG. 18 is a diagram showing an example of the conventional senseamplifier circuit; and

FIG. 19 is a diagram showing an example of the operation waveform of theconventional sense amplifier circuit.

DESCRIPTIONS OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described withreference to the accompanying drawings. Although not particularlylimited, the transistor constituting each block in the embodiments is awell-known CMOS (Complementary MOS transistor) formed on a semiconductorsubstrate made of single crystal silicon by using the known integratedcircuit technology. More specifically, the transistor is formed throughthe process comprising the step of forming a well, a device isolationregion, and an oxide film and the step of forming a gate electrode andfirst and second semiconductor regions to be the source and drain. Thecircuit symbol of MOSFET (Metal Oxide Semiconductor Field EffectTransistor) not provided with a circular mark on its gate represents anN type MOSFET (NMOS) and is distinguished from a P type MOSFET (PMOS)provided with a circular mark on its gate. Hereinafter, the MOSFET issimply referred to as MOS or MOS transistor. However, the presentinvention is not limited to the field effect transistor including anoxide film formed between a metal gate and a semiconductor layer and canbe applied to a circuit using a standard FET such as MISFET (MetalInsulator Semiconductor Field Effect Transistor) having an insulatingfilm between a metal gate and a semiconductor layer.

FIG. 1 is a diagram showing a sense amplifier circuit SA0 according tothe first embodiment of the present invention and a plurality of memorycells MC connected thereto. FIG. 2 is a diagram showing a bank BANKcomprised of sense amplifier circuit arrays SAA-R and ASS-L composed ofthe sense amplifier circuits SA0 according to the first embodiment ofthe present invention, a sub-array SARY0 composed of a plurality ofmemory cells MC, and sub-word arrays SWDA-U and SWDA-D composed of aplurality of sub-word drivers SWD. FIG. 3 is a diagram showing a timingwaveform of the sense amplifier circuit SA0 in FIG. 1. FIGS. 4 and 5 arelayout diagrams of the sense amplifier circuit SA0 shown in FIG. 1.FIGS. 6A to 6D are plan views showing the layout of the plurality ofmemory cells MC shown in FIG. 1. FIG. 7 is a cross-sectional viewshowing a part of the plurality of memory cells MC and the senseamplifier circuit SA0 shown in FIG. 6. FIG. 8 is a block diagram of aDRAM comprised of a plurality of banks BANK shown in FIG. 2.

FIG. 9 is a diagram showing a modified example of the layout of thesense amplifier circuit SA0 shown in FIG. 1. FIG. 10 is a diagramshowing a timing waveform of the sense amplifier circuit SA0 in FIG. 9.FIG. 11 shows a concrete example of a sub-word driver circuit forapplying a negative load to the word line. FIG. 12 is a diagram showingan operation waveform in the second embodiment in which a negativesub-word driver is applied to the sense amplifier. FIG. 13 shows thethird embodiment of the preset invention in which the sense amplifier iscomprised of a plurality of pull-up circuits. FIG. 14 is a diagramshowing an operation waveform of the sense amplifier circuit in FIG. 13.FIG. 15 is a plan view showing the layout of the sense amplifier arraycomprised of a plurality of sense amplifier circuits in FIG. 13. FIG. 16shows the fourth embodiment of the preset invention in which the senseamplifier is comprised of one pull-up circuit and one pull-down circuit.FIG. 17 is a diagram showing an operation waveform of the senseamplifier circuit in FIG. 16. FIG. 18 is a diagram showing aconventional sense amplifier circuit. FIG. 19 is a diagram fordescribing the operation waveform of the conventional sense amplifiercircuit and the malfunction of the circuit.

First Embodiment

The first embodiment of the present invention will be described belowwith reference to FIGS. 1 to 10.

FIG. 1 shows the sense amplifier circuit SA0 comprised of a plurality ofpull-down circuits NDRV0 and NDRV1, one pull-up circuit PDRV, a switchtransistor SHR, a column switch YSW, and a precharge circuit PCH and asub-array SARY0 comprised of a plurality of memory cells MC. Also,eachof the reference symbols indicates common source lines CSN0 and CSN1 fordriving the pull-down circuits NDRV0 and NDRV1, a common source line CSPfor driving the pull-up circuit PDRV, a switch transistor drive linesSHRR and SHRL, a column switch drive line YS, a local data lines LIOTand LIOB, a precharge drive line DLEQ, precharge voltage VDLR, sub-wordlines WL0 to WL3, data lines DLT and DLB, an access transistor TN0, acell capacitor CS0, and a plate electrode PLT.

The plurality of memory cells MC are DRAM memory cells each providedwith the N type channel MOS transistor TN0 and the capacitor CS0. Thepull-up circuit PDRV is comprised of a pair of P type channel MOStransistors, in which a gate of one MOS transistor is connected to adrain of the other MOS transistor. Also, the pull-down circuits NDRV0and NDRV1 are comprised of a pair of N type channel MOS transistors, inwhich a gate of one MOS transistor is connected to a drain of the otherMOS transistor.

As shown in FIG. 1, the transistor constituting the pull-down circuitNDRV0 of the plurality of pull-down circuits in this embodiment has achannel length and a channel width larger than those of the transistorconstituting the pull-down circuit NDRV1. That is, the transistorconstituting the pull-down circuit NDRV0 has a larger driving force(constant). The reason why the constant of the transistor is increasedis that, by increasing the constant, the drive current of the pull-downcircuit NDRV0 can be increased and the offset can be reduced. In thiscase, it is desirable that the NMOS transistor constituting the otherpull-down circuit NDRV1 has a small channel length or has a largechannel width. The reason is as follows. That is, since the transistorconstituting the pull-down circuit NDRV0 has a large channel length, thedrive current of the pull-down circuit NDRV0 is sometimes reduced.Therefore, by reducing the channel length or increasing the channelwidth of the transistor constituting the pull-down circuit NDRV1 to makethe drive current large, the data line can be amplified more rapidly. Asdescribed above, by adding only the pull-down circuit NDRV0 having thesufficiently reduced offset and preamplifying the data line pair to thevoltage difference larger than the offset of the pull-down circuit NDRV1and the pull-up circuit PDRV on the latter stage by driving the commonsource line CSN0, the reading malfunction can be prevented. Note thatthe detail of this operation will be described later.

FIG. 2 shows a concrete example of the bank BANK comprised of senseamplifier arrays SAA-R and SAA-L using a plurality of sense amplifiercircuits SA0 according to this embodiment, a sub-array SARY0, andsub-word drives SWDA-U and SWDA-D. In the example of FIG. 2, commonsource control lines ΦCSN0, ΦCSN1, and ΦCSP are provided for theplurality of sense amplifier circuits SA0 to SA5. The circuits VSS_DRV0,VSS_DRV1, and VDL_DRV for driving the common source lines controlled bythe common source control lines ΦCSN0, ΦCSN1, and ΦCSP are provided foreach sub-array SARY0, and the sense amplifier arrays SAA-R and SAA-Lemploy the so-called distributed drive method. The sub-word driversSWDA-U and SWDA-D are provided for each sub-array SARY0 and drive thesub-word lines WL0, WL1, WL2, WL3, WL4, and WL5 in the sub-array SARY0in response to the selection of the address. VSS-U and VSS-D denote theground voltage.

When compared with the configuration in FIG. 18, the increase of thearea of the sense amplifier circuit SA0 in FIG. 1 is quite small becausethe added transistors are only a pair of NMOS transistors. Therefore, asshown in FIG. 2, the layout with a narrow data line pitch can berealized and the increase of the chip size can be reduced. Also, thesense amplifier circuit SA0 has the same configuration as that of theconventional sense amplifier circuit other than the addition of thepull-down circuit NDRV0. Therefore, when using the sense amplifiercircuit SA0 of this embodiment, the change in the layout and the wiringconfiguration can be reduced to the minimum. Also, although the dataline folding type array configuration in which the data line paircrosses the sub-word lines is shown in FIG. 2, the present invention isnot limited to this. For example, the so-called data line open typearray configuration is available, and the various modifications can bemade within the scope of the present invention.

FIG. 3 shows an operation waveform for describing the operation of thesense amplifier circuit SA0 of this embodiment shown in FIG. 1. First,the precharge drive line DLEQ is asserted to precharge the data linepair to the precharge potential VDLR. There are many methods for drivingthe precharge drive line DLEQ. For example, the method using the rowaddress signal and the sub-array selection signal is available.Similarly, the switch transistor SHRR is negated by using the rowaddress. By doing so, the data line pair of the selection sub-arraySARY0 is electrically connected to the sense amplifier array SAA-R.Next, when the sub-word line WL1 is asserted, the retained signal isoutputted from the plurality of selection memory cells to the data line.For example, the minute signal corresponding to L of the memory cell MCin FIG. 2 is outputted to the data line DLT0. Thereafter, when thecommon source line CSN0 is driven to the ground voltage VSS, the dataline DLT0 is driven to the VSS side more strongly than the data lineDLB0.

Since the channel length and the channel width of the transistor of thepull-down circuit NDRV0 are increased and the offset is sufficientlyreduced, the data line DLT0 can be driven to the VSS of L level moreselectively. After amplifying the data line DLT0 to the voltagedifference larger than the offset of the pull-down circuit NDRV1 and thepull-up circuit PDRV by using the pull-down circuit NDRV0, the commonsource lines CSN1 and CSP are driven to amplify the data line pair DLT0and DLB0 to the low level VSS and to the high level VDL, respectively.The paired common source lines CSN1 and CSP are driven based on the samecontrol signal, and as a result, they are changed from the prechargepotential VDRL to the potentials VSS and VDL at almost the same timing.After the rewriting to the memory cell MC, the sub-word line WL0 isnegated. Thereafter, the common source lines CSN0, CSN1, and CSP areprecharged to the precharge voltage VDLR, the precharge drive line DLEQis asserted, and the data line pair is precharged to the desiredprecharge potential VDLR. This is the operation of the sense amplifierSA0 according to this embodiment of the present invention.

As described above, by adding the pull-down circuit NDRV0 in which theoffset is sufficiently reduced, the reading malfunction can beprevented. Also, the so-called sense amplifier offset margin in thedesign of the signal amount of DRAM can be reduced. Therefore, even whenthe signal amount is reduced due to the reduction of the data linevoltage VDL, since the above-described sense amplifier offset margin isalmost unnecessary, the stable read operation can be realized. Morespecifically, the low-voltage operation can be realized and the lowpower consumption can be achieved. Also, even if the data line length isincreased, the stable read operation can be realized. The reason will bebriefly described below. Usually, when the data line length isincreased, the parasitic capacitance of the data line is increased.Therefore,the signal amount outputted to the data line is reduced. As aresult, the voltage difference applied to the sense amplifier circuit isreduced and the operation of the sense amplifier becomes unstable.However, when the sense amplifier circuit SA0 according to thisembodiment is used, even if the voltage difference applied to the senseamplifier circuit SA0 is small, the data line can be preamplifiedbecause the offset of the pull-down circuit NDRV0 is sufficiently small.More specifically, since it is possible to preamplify the data line tobe larger than the offset of the pull-down circuit NDRV1 and the pull-upcircuit PDRV by using the pull-down circuit NDRV0, the stable readoperation can be realized even if the data line length is increased. Inother words, the highly-integrated semiconductor memory device with alarge memory occupancy can be realized.

FIGS. 4 and 5 are plan views showing the layout of the sense amplifierarray SAA-R comprised of a plurality of sense amplifier circuits SA0 inFIG. 1. Some of the symbols indicating the parts enclosed by dottedlines correspond to each circuit constituting the sense amplifiercircuit SA0 in FIG. 1. The symbols other than these, that is, YS0 to YS2denote the column switch drive lines and LIO0T, LIO0B, LIO1T, and LIO1Bdenote the local data lines. Note that FIG. 5 shows an example of thewiring layout of the contact V2 and the second wiring layer M2. Also,the symbols in FIGS. 4 and 5 denote the gate contact FGCNT whichconnects the gate electrode and the first wiring layer M1 (data line),the diffusion layers LN and LP, the gate electrode FG, the diffusionlayer contact LCNT which connects the diffusion layers LN and LP and thewiring layer M1, and the contact V2 which connects the second wiringlayer M2 and the third wiring layer M3. Note that the contact V1 whichconnects the first wiring layer M1 and the second wiring layer M2 is notillustrated. Also in FIG. 4, the common source drives VSS_DRV0,VSS_DRV1, and VDL_DRV are used to drive the common source lines CSN0,CSN1, and CSP and are provided for a plurality of sense amplifiercircuits SA0 to SA5. That is, an example of the layout employing theso-called distributed drive method is shown in FIG. 4.

More specifically, for one sub-array SARY0, a plurality of circuitsVDL_DRV, VSS_DRV0, and VSS_DRV1 for driving the common source line aredispersedly arranged between a plurality of pull-down circuits NDRV0 andpull-down circuits NDRV1 operated as a pair and a plurality of pull-upcircuits PDRV. The control lines ΦCSN0, ΦCSN1, and ΦCSP for controllingthe drive circuits VDL_DRV, VSS_DRV0, VSS_DRV1 extend in the samedirection and are formed of the same wiring layer as the power sourceline for supplying the precharge voltage VDLR, the local data linesLIOT, LIO0T, LIO1T, LIOB, LIO0B, and LIO1B, the common source linesCSN0, CSN1, and CSP, and the power source line for supplying the dataline voltage VDL and the ground voltage VSS. These wirings are formed inthe same direction as that of the wordline. The column switch drivelines YS0 to YS2 are connected to the column switch YSW via the contactV2, formed in the third wiring layer M3 on the second wiring layer M2,and extend in the same direction as the data line.

As described above, since the drive circuits are dispersedly arranged ineach of the sense amplifier arrays SAA-R corresponding to the sub-arraySARY0, the common source line can be driven at high speed. Also, sincethe drive circuits are arranged between the pull-down circuit NDRV1 andthe pull-up circuit PDRV, the efficient layout can be realized. Notethat the description of some part of the wiring layer is omitted inorder to prevent the drawing from being complicated.

As shown in FIGS. 4 and 5, the added circuit in the sense amplifiercircuit SA0 in FIG. 1 is only the pull-down circuit NDRV0. Therefore, asis apparent from FIG. 4, the increase of the area of the sense amplifiercircuit SA0 is small. Also, since the symmetric property of the layoutis excellent, the data line noise is small. Further, since the layoutsimilar to the conventional pull-down circuit NDRV1 is possible and theadditional wiring required when adding the circuit is only the commonsource line CSN0, the circuit can be easily realized. The transistors ofthe pull-down circuits NDRV0 and NDRV1 and the pull-up circuit PDRV havethe ring-shaped gates. By the ring-shaped gate electrodes, the offset ofthe sense amplifier circuit can be further reduced.

Note that the shape of the gate electrode FG of the pull-down circuitNDRV0 is illustrated as a ring shape in FIG. 4. However, the presentinvention is not limited to this. The gate electrode FG with a U shapeand a rectangular shape is also available. Also, it is also preferableto operate the sense amplifier circuit SA0 while reducing the drivespeed of the common source line CSN0 shown in FIG. 3 by making thechannel width of the common source driver VSS_DRV0 narrower than thatshown in FIG. 4 or driving the common source control line ΦCSN0 slowly.By doing so, even when the offset of the pull-down circuit NDRV0 isincreased, the data line DLT0 can be preamplified accurately. Also,though not shown in the drawing, it is also preferable to use theso-called overdrive method in combination, in which the common sourceline CSP is boosted to be higher than the high level VDL of the dataline. Also in this case, the effect of the low-voltage operation and thehigh-speed operation can be achieved. As described above, it is needlessto say that various modifications can be made within the scope of thepresent invention.

FIG. 6 is a plan view showing the layout of the memory cell MC and thesense amplifier arrays SAA-L and SAA-R connected thereto. The accesstransistor TN0 is comprised of the sub-word line WL and the diffusionlayer ACT, and the cell capacitor CS0 is comprised of the storage nodeSN and the plate electrode PLT. Other symbols denote the cell contactCCNT for connecting the diffusion layer ACT to the wiring and thecontact thereon, the data line contact DLCNT for connecting the datalines DLT and DLB to the cell contact CCNT, and the storage node contactSNCNT for connecting the landing pad LPAD to the cell contact CCNT. Inthis case, the landing pad LPAD is a contact for connecting the storagenode SN and the storage node contact SNCNT and can optimize the locationof the cell capacitor CS0. Therefore, the surface area of the cellcapacitor CS0 can be increased. Of course, if the capacity of the cellcapacitor CS0 can be sufficiently secured, the landing pad LPAD is notnecessarily required. In such a case, since the number of process stepscan be reduced, the required cost can be reduced.

Also, various modifications of the layout of the memory cell MC can bemade as shown in FIG. 6. For example, FIG. 6A shows the so-called foldeddata-line configuration, in which the scaling down is easy because thediffusion layer ACT has a simple rectangular shape. Also, FIG. 6B showsthe pseudo folded data-line configuration. The difference from FIG. 6Ais that the diffusion layer ACT is laid diagonally to the sub-word lineWL. Therefore, since the effective channel width can be increased, theON-current of the access transistor TN0 can be increased. When using itin combination with the sense amplifier circuit SA0 according to thisembodiment, the semiconductor memory device capable of achieving furtherhigh-speed operation can be realized. FIGS. 6C and 6D show the opendata-line configuration. When compared with the folded data-lineconfiguration, the cell area can be reduced. Since the data line of FIG.6C has a wide pitch, the parasitic capacitance of the data line can bereduced. Therefore, when using it in combination with the senseamplifier circuit SA0 according to this embodiment, thehighly-integrated semiconductor memory device capable of achievingfurther low-voltage operation can be realized. Since the cell area inFIG. 6D is smaller than that in FIG. 6C, when using it in combinationwith the sense amplifier circuit SA0 according to this embodiment, thefurther highly-integrated semiconductor memory device can be realized.

The layout applicable to the sense amplifier of the present invention isnot limited to them. For example, the layout in which the diffusionlayer ACT laid diagonally to the sub-word line WL in the open data-lineconfiguration of FIG. 6D is changed to be orthogonal to the sub-wordline WL like in FIG. 6A is also available. In such a case, the scalingdown can be easily performed because of the rectangular shape. Further,by applying the low level VSS to the sub-word line WLA while commonlyusing the diffusion layer ACT of the adjacent left and right cells ofthe sub-ward line SWLA, the device isolation is enabled. In this case,since it is unnecessary to form the device isolation region made ofinsulator extending in a direction parallel to the data line, the numberof process steps can be reduced and the required cost can be reduced.

FIG. 7 is a cross-sectional view showing a part of the plurality ofmemory cells MC and the sense amplifier circuit SA0 shown in FIG. 6. InFIG. 7, the second wiring layer M2, the third wiring layer M3, the Pwell substrate PW, the N well substrate NW, the deep N well substrateDNWELL, and the P type substrate PSUB are provided. Note that theforming method of these components is the same as that of the standardsemiconductor memory device, in particular, the so-called generalpurpose DRAM. Therefore, the detail description thereof is omitted here.Also, the configuration of the cell capacitor CS0 is not limited tothis. For example, a crown-like shaped capacitor and other capacitor areavailable as the cell capacitor CS0.

As described above, since only the two NMOS transistors and the wiringfor the common source line CSN0 are added in the sense amplifier circuitSA0 of this embodiment, the circuit can be easily realized. Thediffusion layer of the NMOS transistor of the pull-down circuit NDRV0can be formed in the same P type well PW as the diffusion layer of thetransistor in the memory cell and the diffusion layer of the NMOStransistor of the pull-down circuit NDRV1. Also, since it is unnecessaryto additionally arrange the wiring on the sub-array SARY0, the wiringnoise does not occur. Therefore, it does not cause any problem for thememory operation.

FIG. 8 is a block diagram showing an example of the DRAM comprised of aplurality of banks BANK shown in FIG. 2. The symbols in FIG. 8 denotethe address buffer ADDRESS BUFFER, the column address buffer COLUMNADDRESS BUFFER, the column address counter COLUMN ADDRESS COUNTER, therow address buffer ROW ADDRESS BUFFER, the refresh counter REFRESHCOUNTER, the bank select BANK SELECT, the mode resister MODE RESISTER,the row decoder ROW DEC, the column decoder COLUMN DEC, the main senseamplifier SENSE AMP, the memory cell array MEMORY CELL ARRAY, the datainput buffer Din BUFFER, the data output buffer Dout BUFFER, the databuffer DQS BUFFER, the delay locked loop DLL, the control logic CONTROLLOGIC, the clocks CLK and /CLK, the clock enable signal CKE, the chipselect signal /CS, the row address strobe signal /RAS, the columnaddress strobe signal /CAS, the write enable signal /WE, the data writesignal DW, the data strobe signal DQS, and the data DQ. Note that sincethe control method of these circuits and signals is the same as that ofthe well-known SDRAM, the detail description thereof is omitted here. Byconstituting the bank BANK shown in FIG. 8 by using the sense amplifiercircuit SA0 of this embodiment, a semiconductor memory device such asthe synchronous dynamic memory SDRAM can be realized. Of course, byusing the sense amplifier circuit SA0 in this embodiment, theabove-described effects of the low-voltage operation and the like can berealized. Also, the configuration of the blocks is not limited to thatshown in FIG. 8. For example, the configuration in which the number ofmemory cell arrays MEMORY CELL ARRAY is increased is also available, andvarious modifications can be made within the scope of the presentinvention.

FIG. 9 is a plan view showing a modified example of the layout of thesense amplifier array SAA-R comprised of the plurality of senseamplifier circuits SA0 shown in FIG. 1. The difference from FIG. 4 isthat the gate electrode of the pull-down circuit NDRV2 has a rectangularshape not a ring shape. When the ring-shaped gate electrode is used likein the case of FIGS. 4 and 5, the drive current of the pull-down circuitNDRV1 is sometimes reduced. In such a case, by using therectangular-shaped gate electrode as shown in FIG. 9, the drive currentcan be increased and the more stable operation can be realized. Notethat since the layout of the contact V1, the second wiring layer M2, andthe contact V2 is almost the same as that of FIG. 5, the descriptionthereof with reference to the drawing is omitted here.

FIG. 10 shows an operation waveform when the layout of the senseamplifier in FIG. 9 is applied. Since the operation is basicallyidentical to that of FIG. 3, the detail description thereof is omitted.The difference from FIG. 3 is as follows. That is, when driving thepull-down circuit NDRV2 and the pull-up circuit PDRV, since the drivecurrent of the pull-down circuit NDRV2 is larger than that of thering-shaped pull-down circuit NDRV1 of FIG. 4, the preamplified dataline pair can be amplified more rapidly. Consequently, the semiconductormemory device capable of achieving the high-speed operation can berealized. In addition, although the case where the pull-down circuitNDRV2 is formed by using the rectangular gate electrode FG has beenshown in FIG. 9, the rectangular gate electrode FG can be of courseapplied to the pull-up circuit PDRV. Also in this case, since the drivecurrent of the pull-up circuit PDRV can be increased, the high-speedoperation similar to the case described above can be realized. These arethe descriptions of the first embodiment.

Second Embodiment

The case where the ground voltage VSS is applied to the sub-word line WLof the memory cell MC at the time of non-selection has been described inthe first embodiment. However, it is also possible to apply the negativevoltage.

FIGS. 11 and 12 show the case where the negative word driver NSWD isapplied to the sense amplifier circuit SA0 of this embodiment.

FIG. 11 shows a modified example of the sub-word driver SWD constitutingthe sub-word array SWDA-U and SWAD-D in FIG. 2. The. symbols in FIG. 11denote the word line voltage VPP, the negative word line voltage VKK,the main word line MWL, the sub-word line control signals FX and FXB,and the inverters INV0 and INV1. Since the control method of thesesignals is the same as that of the standard sub-word driver, thedescription thereof is omitted here.

FIG. 12 is a diagram showing the operation waveform in the case wherethe negative sub-word driver NSWD in FIG. 11 is applied to the senseamplifier circuit SA0 of this embodiment. The difference from theoperation waveform in FIG. 3 is that the word line voltage at the timeof non-selection is the negative voltage lower than the potential fordriving the pull-down circuit. As described above, by applying thenegative voltage at the time of non-selection of the word line, thethreshold voltage of the access transistor can be effectively increased.In other words, even when the threshold voltage of the access transistorTN0 is set low, the problem of the degradation of the so-calledretention characteristics of the DRAM does not occur. More specifically,since the impurity concentration of the channel region can be reduced,the junction electrical field between the diffusion layer ACT and the Pwell substrate PW can be reduced. As a result, since the leakage currentthrough the diffusion layer ACT can be reduced, the semiconductor memorydevice capable of achieving the further low-power consumption can berealized. In addition, since the impurity concentration can be reduced,the variation in threshold voltage of the access transistor TN0 can bealso reduced. As a result, it becomes unnecessary to set the word linevoltage VPP higher than necessary in the write operation. Morespecifically, since it becomes possible to reduce the thickness of thegate insulating film of the access transistor TN0, the further scalingdown can be performed and the further highly-integrated semiconductormemory device can be realized.

Also, it is needless to say that the more effects can be obtained byusing the sense amplifier circuits of this embodiment in combination.More specifically, as described above, the sufficiently stable readoperation can be realized in the sense amplifier circuit SA0 of thisembodiment even when the read signal amount is reduced by the voltagereduction. Furthermore, when the sense amplifier circuit SA0 of thisembodiment is used in combination with the layout to which therectangular gate electrode is applied, the high-speed operation can beof course realized. Also, by using the negative sub-word driver NSWD,the scaling down of the access transistor TN0 can be realized. That is,since the further scaling down of the memory cell MC can be realized, itis possible to reduce the parasitic capacitance of the data line. As aresult, the highly-integrated semiconductor memory device capable ofachieving further low-voltage operation can be realized.

Third Embodiment

The case where a plurality of pull-down circuits are applied has beendescribed in the first and second embodiments. In this case, the size ofthe offset of the pull-down circuit determines whether the stable readoperation is enabled or the malfunction occurs. Therefore, since it isunnecessary to reduce the offset of the pull-up circuit more thannecessary, the number of masks required to form the PMOS transistor canbe reduced by using the so-called buried channel type PMOS transistor.

Of course, the present invention is not limited to the embodimentsdescribed above, and it is also preferable to form the sense amplifiercircuit SA0 by using a plurality of pull-up circuits. In this case, itis preferable that the so-called dual gate transistor instead of theso-called buried channel type transistor is used as the PMOS transistorconstituting the pull-up circuit. By doing so, though the number ofmasks required to form the PMOS transistor is increased, since thetransistor configuration is simplified, the variation in thresholdvoltage of the PMOS transistor can be reduced.

FIG. 13 is a circuit diagram of the sense amplifier circuit SA0 using aplurality of pull-up circuits, FIG. 14 is a diagram showing theoperation waveform thereof, and FIG. 15 is a plan view showing thelayout thereof.

As shown in FIG. 13, the sense amplifier circuit SA0 of this embodimentis comprised of a plurality of pull-up circuits PDRV0 and PDRV1. Sinceother components are the same as those in the above-describedembodiments, the description thereof is omitted. Also, similar to theabove-described embodiments, the PMOS transistor constituting thepull-up circuit PDRV0 shown in FIG. 13 has a channel length and achannel width larger than those of the PMOS transistor constituting thepull-up circuit PDRV1. That is, the transistor constituting the pull-upcircuit PDRV0 has a larger driving force (constant). The reason why theconstant of the transistor is increased is that it is necessary tosufficiently reduce the offset of the pull-up circuit PDRV0 andsufficiently preamplify the data line pair to the voltage differencelarger than the offset of the pull-up circuit PDRV1 and the pull-downcircuit NDRV driven in the latter stage. By doing so, the readingmalfunction can be prevented.

FIG. 14 is a diagram showing the operation waveform for describing theoperation of the sense amplifier circuit SA0 in FIG. 13. Since theoperation is basically identical to that of FIG. 3, the detaildescription thereof is omitted. The difference from FIG. 3 is asfollows. That is, after the minute signal difference dVsig is outputtedto the data line pair, the common source driver VDL_DRV is asserted todrive the common source line CSP0 to the data line voltage VDL, and thepull-up circuit PDRV0 is activated to preamplify the data pair. By doingso, the data line DLB0 is driven to the VDL side more strongly than thedata line DLT0. Next, by driving the pull-up circuit PDRV1 and thepull-down circuit NDRV, the data line pair is amplified to the highlevel VDL and the low level VSS. This is the operation of the senseamplifier circuit SA0 in this third embodiment.

FIG. 15 is a plan view showing an example of the layout of the senseamplifier array SAA-R comprised of a plurality of sense amplifiercircuits SA0 in the third embodiment. The difference from the layout inFIG. 4 is that a plurality of pull-up circuits PDRV0 and PDRV1 and thecommon source drivers VDL_DRV0 and VDL_DRV1 for driving them areprovided. Note that since other components are the same as those in theabove-described embodiments, the description thereof is omitted. Also,since the layout of the contact V1, the second wiring layer M2, and thecontact V2 is the same as that of FIG. 4, the illustration thereof isomitted here. As shown in FIG. 15, also in the case where a plurality ofpull-up circuits are used, the symmetric property of the layout isexcellent and the data line noise is small. Also, since the number ofadded transistors is only two and only a little wiring is added, it canbe realized easily.

In the foregoing, the third embodiment has been described with referenceto FIGS. 13 to 15. However, it is needless to say that the presentinvention is not limited to this. For example, the pull-up circuit witha rectangular gate electrode as shown in FIG. 9 can be applied and thenegative sub-word driver NSWD as shown in FIG. 2 can be used. Inaddition, though FIG. 15 shows an example of the layout employing theso-called distributed driver method similar to FIG. 4, the layout is notlimited to this. It is also preferable to use the so-called overdrivemethod in which the common source line CSP0 is boosted to be higher thanthe high level VDL of the data line in combination. It is needless tosay that the effect as described above can be obtained also in thiscase. The various modifications can be made within the scope of thepresent invention.

Fourth Embodiment

In the first to third embodiments, the sense amplifier circuit includesa plurality of pull-down circuits or a plurality of pull-up circuits.However, if the high-speed operation is not required, the senseamplifier circuit comprised of one pull-down circuit and one pull-upcircuit is also available in some cases. In such a case, in order toreduce the offset, the channel length and the channel width of thetransistor constituting the pull-down circuit and the pull-up circuitare increased. Furthermore, the data line pair is preamplified to belarger than the offset of the pull-up circuit by driving, for example,the pull-down circuit prior to the pull-up circuit.

FIG. 16 is a diagram showing the sense amplifier circuit SA0 in thisembodiment. The difference from the above-described embodiments is thatthe sense amplifier circuit is comprised of one pull-down circuit andone pull-up circuit. Also, since other components in FIG. 16 are thesame as those of the above-described embodiments, the descriptionthereof is omitted here. As described above, since it is not necessaryto add any circuit to the conventional sense amplifier circuit in thisembodiment, the area of the sense amplifier circuit SA0 can be reducedin comparison to the above-described embodiments. Also, since it is notnecessary to add any driving signal, the addition of the wiring is notrequired and the process cost can be reduced. More specifically, thesemiconductor memory device capable of achieving both the stable readingoperation and the area reduction of the sense amplifier can be realized.

FIG. 17 is a diagram showing the operation waveform of the embodimentshown in FIG. 16. Since the operation is basically identical to that ofFIG. 3, the detail description thereof is omitted. The difference fromFIG. 3 is as follows. That is, after the minute signal difference dvsigis outputted to the data line pair, the common source driver VSS_DRV isasserted to drive the common source line CSN to VSS, and the pull-downcircuit NDRV is first activated. After the data line DLT0 issufficiently amplified to be larger than the offset of the pull-upcircuit PDRV, the common source driver VDL_DRV is asserted to drive thecommon source line CSP to the high level VDL, and the pull-up circuitPDRV is activated. Since the data line DLT0 is sufficiently amplified bythe pull-down circuit NDRV activated in advance, the pull-up circuitPDRV can amplify the data line DLB0 to the high level VDL withoutmalfunction. This is the operation of the sense amplifier SA0 in thisfourth embodiment.

The pull-down circuit NDRV is first activated in this embodiment.However, it is needless to say that the same effect can be obtained evenwhen the pull-up circuit PDRV is first driven. Also, when using it incombination with the above-described embodiments, the low-voltageoperation and the higher integration can be achieved. As describedabove, various modifications can be made also in this embodiment withinthe scope of the present invention.

Also, in the description of the first to fourth embodiments, the onetransistor DRAM cell is used as an example of the memory cell MC.However, the two transistor DRAM cell, that is, the so-called twin cellis also available. Also, the so-called OR cell which obtains the logicalsum of two memory cells is also available when two memory cells areused. Of course, instead of the DRAM cell, the six-transistor staticrandom access memory is also available, and various types of memorycells can be used in combination with the sense amplifier circuit of thepresent invention.

Furthermore, as an example of the method for reducing the offset, thechannel length and the channel width of the transistor are increased.However, the present invention is not limited to this. For example, themethod in which the impurity concentration of the transistor substrateconstituting the sense amplifier is set low so as to reduce thevariation in threshold voltage due to the impurity fluctuation is alsoavailable. Also, it is preferable to constitute the sense amplifierwhile reducing the threshold voltage of the NMOS transistor and the PMOStransistor which constitute the sense amplifier circuit. In this case,since the voltage applied to the sense amplifier circuit is effectivelyincreased, the further high-speed operation can be realized. Inaddition, since the impurity concentration is reduced when the thresholdvoltage is reduced, the variation in threshold voltage can be reduced.Therefore, since the offset can be reduced, it is unnecessary toincrease the driving force (constant) of the transistor, that is, thechannel length and the channel width of the pull-down circuit and thepull-up circuit more than necessary. More specifically, it is possibleto reduce the area of the sense amplifier circuit. Alternatively, it isalso preferable to dynamically change the substrate voltage of thetransistor constituting the above-described sense amplifier circuit atthe time of the read operation. Also in this case, since the voltagedifference applied to the sense amplifier circuit is effectivelyincreased, the further high-speed operation can be realized.

For dynamically changing the substrate voltage of the transistor, theadditional circuit is required. However, since it can be realized by ausual circuit modification, the illustration thereof is omitted here.Also in this case, it is necessary to apply different substrate voltagesto the memory cell part and the sense amplifier part. However, since itcan be realized by a simple circuit modification, the illustrationthereof is omitted here. As described above, various modifications canbe made in the sense amplifier circuit of the present invention inaccordance with its purposes such as the low-voltage operation, thehigh-speed operation, and the higher integration.

1. A semiconductor device, comprising: a memory array having a pluralityof word lines, a plurality of data lines, and a plurality of memorycells arranged at intersections of the plurality of word lines and theplurality of data lines; and a plurality of sense amplifier circuitsconnected to the plurality of data lines, wherein each of the pluralityof sense amplifier circuits is provided with a first MISFET pair of afirst conductivity type in which a gate of one MISFET is directlyconnected to a drain of the other MISFET, a second MISFET pair of thefirst conductivity type in which a gate of one MISFET is directlyconnected to a drain of the other MISFET, and a third MISFET pair of asecond conductivity type in which a gate of one MISFET is directlyconnected to a drain of the other MISFET, and wherein each of gatelengths of the first MISFET pair is longer than each of gate lengths ofthe second MISFET pair.
 2. The semiconductor device according to claim1, wherein the first conductivity type is an N type, wherein sources ofthe first MISFET pair are connected to a first source line, whereinsources of the second MISFET pair are connected to a second source line,wherein sources of the third MISFET pair are connected to a third sourceline, and wherein the first source line is driven before the secondsource line is driven.
 3. The semiconductor device according to claim 2,wherein a voltage of the second source line and a voltage of the thirdsource line are changed, in response to the same signal, from a firstvoltage to a second voltage and from the first voltage to a thirdvoltage, respectively.
 4. The semiconductor device according to claim 2,further comprising: a first circuit for driving the second source linefrom a first voltage to a second voltage; and a second circuit fordriving the third source line from the first voltage to a third voltage,wherein the second MISFET pair is arranged between the first MISFET pairand the third MISFET pair, and wherein the first circuit and the secondcircuit are arranged between the second MISFET pair and the third MISFETpair.
 5. The semiconductor device according to claim 2, furthercomprising: wherein the plurality of sense amplifier circuits arearranged along two opposed sides of the memory array, and whereinsources of the first MISFET pairs of sense amplifier circuits arrangedon one of the sides are commonly connected to the first source line. 6.A semiconductor device, comprising: a memory array having a plurality ofword lines, a plurality of data lines, and a plurality of memory cellsarranged at intersections of the plurality of word lines and theplurality of data lines; and a plurality of sense amplifier circuitsconnected to the plurality of data lines, wherein each of the pluralityof sense amplifier circuits is provided with a first MISFET pair of afirst conductivity type in which a gate of one MISFET is directlyconnected to a drain of the other MISFET, a second MISFET pair of thefirst conductivity type in which a gate of one MISFET is directlyconnected to a drain of the other MISFET, and a third MISFET pair of asecond conductivity type in which a gate of one MISFET is directlyconnected to a drain of the other MISFET, and wherein each of gatewidths of the first MISFET pair is wider than each of gate widths of thesecond MISFET pair.
 7. The semiconductor device according to claim 6,wherein the first conductivity type is an N type, wherein sources of thefirst MISFET pair are connected to a first source line, wherein sourcesof the second MISFET pair are connected to a second source line, whereinsources of the third MISFET pair are connected to a third source line,and wherein the first source line is driven before the second sourceline is driven.
 8. The semiconductor device according to claim 7,wherein a voltage of the second source line and a voltage of the thirdsource line are changed, in response to the same signal, from a firstvoltage to a second voltage and from the first voltage to a thirdvoltage, respectively.
 9. The semiconductor device according to claim 7,further comprising: a first circuit for driving the second source linefrom a first voltage to a second voltage; and a second circuit fordriving the third source line from the first voltage to a third voltage,wherein the second MISFET pair is arranged between the first MISFET pairand the third MISFET pair, and wherein the first circuit and the secondcircuit are arranged between the second MISFET pair and the third MISFETpair.
 10. The semiconductor device according to claim 7, furthercomprising: wherein the plurality of sense amplifier circuits arearranged along two opposed sides of the memory array, and whereinsources of the first MISFET pairs of sense amplifier circuits arrangedon one of the sides are commonly connected to the first source line.